Expansion vessel pre-pressure............information please

[Cliveshep]

Could someone with a bit of knowledge on pressurised water systems help out here please. I've got a pressurised water system with one pump running hot and cold to sink, basin and shower with a calorifier in the system. To smooth out the initial "spurt" I'm proposing to fit an expansion vessel, currently there isn't one installed. I've got a stainless steel one, approx 200 high x 125mm diameter spare from a site clearance, it has a car type valve fitted so can be pumped up.

Can any one advise what pressure it should be pumped up to prior to installation? Before you ask the obvious, sorry but I have absolutely no idea what the water pump is apart from being a Jabsco with a pressure switch fitted to a 30ft ex hire boat. I'm at home and the boat is miles away mouldering on it's mooring! The pressure vessel was originally intended to be fitted in conjunction with a combi boiler on the domestic side of an apartment installation.

 

[sailorman]

1 bar

 

[mikehibb]

check the Jabsco site:
clicky

you can find pdf data sheets like this

another clicky

 

[Billjratt]

Has it got a diaphragm - and is it intact? Otherwise just fit it like a standard Jabsco and let the water-pump do the pressurising.

 

[Cliveshep]

Ok, 1 bar........errr.....whats that translated into PSI please? It is by the way a variable type pump, i.e pumps slow on slow water use, speeding up if the tap is fully open.

 

[Cliveshep]

Thanks for that but I'm not sure looking quickly (the kids are demanding I get back off the PC) it answers my question.

 

[sailorman]

32 psi ( resting ) before you pressurize with the water pump

 

[Cliveshep]

Hi there, answer yes, it has a spring/air pressured diaphragm and the pump will compress the diaphragm, it is what pressure I need to put in it before I turn the pump on I wanted to know as I assume it should be pretty much fully flexed when the pump has achieved the preset pressure and switched off. I doubt that the pressure needed in it for a domestic mains situation would be the same as with a water pump, well, actually, I don't know.

 

[Cliveshep]

Magic, many thanks, by the way, have I been "Lakesailored"?

 

[sailorman]

possibly BANNED /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

 

[pennycar9]

No its not. I think you will find 1 bar =14.7PSI

 

[sailorman]

yes 2.4 is about 32 psi /forums/images/graemlins/blush.gif

 

[Bilgediver]

yes 2.4 is about 32 psi
**********************
Yes we know it is and as the operating pressure is about this then the bottle should only be pumped to 1 bar or it will not do its job

 

[Cliveshep]

Right then, just to dot the "i"s and cross the "t"s on this, I pre-pressurise the expansion vessel to 14.5 psi?

Final answer and not phoning friend?

Kids have now given up on getting their turn and b@ggered off to bed in double hissy fits!

 

[Eeyore]

Yes......as a starting point! You can adjust the pressure to suit your particular pump and system when you switch it all on again. Shouldn't really be pressurised more than 1 bar though when the pump is disconected and the water pressure in the system is released.

1 bar = 1 atmosphere = 14.5psi (approx)

 

[sailorman]

a bicycle pump is sufficient. i re-pressurized my system 3 wks ago

 

[Cliveshep]

Terrific, many thanks to all and I'll get down and get on with it (but not tonight!)

 

[mikemonty]

I'm afraid I'm not being very constructive here but...
1 Bar is not specific enough -
1 Bar "Absolute" would be 14.5 psi "Absolute" which doesn't make much sense in htis context as it is .2 of a psi below normal atmospheric pressure (in other words a slight vacuum)
Given this fact, it is probable that you intended:-
1 Bar "Gauge" which is 1 bar (14.5 psi) above atmospheric (14.7 psia ) therefore 29.2 psia.

To the OP:-
Most of the stuff that I found by googling turned up suggested somewhere between 2 and 3 bar absolute for a settle-out pressure - but I suspect it is not critical - just don't over pressure it!

 

[sailorman]

its only a friggin accumulator tank. not a scientific instrument /forums/images/graemlins/crazy.gif

 

[DownWest]

I used a lot of these on house water systems, still have one here. I bar/ 15psi is enough. Though I wonder if that is too much on a boat system.
A
To add: Central heating systems work at 1 bar (approx) while house systems use 2 to 3 bar or more. So your expansion tank will be pre pressured to a lower figure than 1 bar in it's original use.